The present invention relates to an improved clamp mechanism and method for operating same and, more particularly, an improved clamp mechanism for use in a reciprocating press such as an injection molding machine wherein a fluid link is employed to affect the clamping of a pair of platen halves together.
Toggle clamps used in presses for injection molding, compression molding, die casting and the like are well-known in the art. A typical toggle clamp mechanism is disclosed in U.S. Pat. No. 3,117,348 to Rees and Schad which is assigned to the assignee of the present invention. As disclosed in U.S. Pat. No. 3,117,348, the toggle mechanism is actuated by a connecting rod which works in conjunction with a rotating disk which is driven by a variable speed drive motor. The mechanism is designed so as to allow for the disk to rotate always in the same direction. In order to actuate the toggle mechanism a pinion gear provided on the disk engages the drive shaft of the variable speed motor by means of a clutch. The disk rotates so as to push and pull the toggle system which is articulated by the connecting rod which links the rotating disk with the center pin of the toggle system. When the toggle system is stretched out the platens of the press abut each other and are in their locked position. In the stretched out position, the pinion is unclutched from the drive motor and a brake is applied so that the connecting rod and the corresponding toggle mechanism, which are now in their stretched out position, are immobilized so as to lock the platens in place. The locking force is transmitted linearly from the space between the platens onto the abutment holding the toggle system and any movement of the center link of the toggle system, which would result in the release of the clamping action, is absorbed by the fixed position of the disk pinion and connecting rod thereby resulting in the entire assembly being immobilized. As can be seen from the foregoing the opening and closing movements of the platens is effected by the rotating disk via the connecting rod and linkage system whereby the connecting rod holds and pushes the toggle links corresponding to the opened and closed positions of the platens. The rotating disk is stopped by the clutch and brake arrangement in one or both of the positions corresponding to the fully opened and fully locked positions of the platens.
The primary advantage of the toggle system as described above is its great speed, that is, the opening and closing sequence of the platens is carried out without the necessity of reversing the actuating element as is customarily required by other known toggle systems which are typically actuated by reciprocating cylinders. While the above-described system has been used extensively in industry it nevertheless has certain drawbacks and disadvantages when employed in systems requiring locking forces in excess of 250 tons. In particular, it has been found that the transmission system tends to be overstressed and therefore not function with the desired degree of reliability when attempts are made to increase the locking force that may be exerted by the system. In addition, the drive provided by a motor with a conventional variable speed pulley drive tends to be oversized and the drive itself not adequate for the operation of large clamps thereby requiring the use of alternate mechanicam drives which tend to be large, occupy a great deal of space in a given machine and quite expensive. Finally, the clutch and brake system employed is not designed for highly stressed conditions. To summarize, when working with locking forces in excess of 250 tons the reliability of the system described above is limited.
Naturally it would be highly desirable to provide a clamp mechanism suitable for use in reciprocating presses and the like which overcome the problems noted above with regard to prior art clamp mechanisms.
Accordingly, it is the principal object of the present invention to provide a novel transmission suitable inter alia for use with clamp mechanisms for selectively locking and unlocking a member in place.
It is a particular object of the present invention to provide a clamp mechanism as aforesaid which is particularly useful in reciprocating presses such as pressure molding machines.
It is a further object of the present invention to provide a transmission as aforesaid which employs a fluid link for positioning a member in place.
It is a still further object of the present invention to provide a clamping mechanism as aforesaid in a reciprocating press wherein means are provided for sensing an obstruction between the relatively movable press members.
It is another still further object of the present invention to provide a clamp mechanism as aforesaid which is of simple construction, economic to manufacture and easily used with a high degree of reliability.
Further objects and advantages of the present invention will appear hereinbelow.